The present invention relates generally to semiconductor etching techniques and more particularly to using aluminum as an etch mask and etchstop for tungsten etchback.
Various process techniques have been proposed for the planarization of contacts and vias filled with non-selective CVD tungsten. However the prior art processes do not, in practice, completely remove the CVD tungsten until lead definition. One of the reasons for this is that a high selectivity of CVD tungsten over oxide is difficult to obtain. Thus a conventional etchback step would result in thinning of the oxide over the active devices if the CVD Tungsten is etched completely during the planarization etch. Prior art attempts to increase the oxide layer thickness to allow for the over etching of the oxide also have proved unsatisfactory. One of the problems with this technique is the difficulty in controlling how much tungsten is left during the CVD tungsten planarization and accordingly how much must be etched away during the lead definition etch.